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The Status, Threats, and Resilience
of Reef-Building Corals
of the Saudi Arabian Red Sea
Andrew W. Bruckner and Alexandra C. Dempsey
Abstract
The Saudi Arabian Red Sea (SARS) contains diverse shallow water coral reef systems that
include attached (fringing and dendritic reefs) and detached (platform, patch, tower, ribbon,
and barrier reefs) reef systems extending up to 90 km offshore. To better understand the
current status of coral reefs in SARS, the Living Oceans Foundation conducted assessments of
representative reef environments in the Farasan Islands (2006), Ras Al-Qasabah (2007),
Al Wajh and Yanbu (2008), and the Farasan Banks (2009). A combination of belt transects
and quadrats was used to assess the diversity, size structure, partial mortality, condition, and
recruitment of the dominant reef-building corals. Most sites had high structural complexity,
with up to 52 genera of scleractinian corals recorded from a single region. Living corals varied
in abundance and cover by region, habitat, and depth, with the highest species richness
documented in the south (Farasan Banks), followed by Al Wajh and Yanbu and lowest at Ras
Al-Qasabah. On most reefs, a single species was dominant. The reef architecture was
constructed by massive and columnar Porites, with unusually large (1–4 m diameter) colonies
in shallow water (up to 80 % live cover in 2–10 m depth) and a deeper reef Porites framework
that was mostly dead. Porites lutea was the single most abundant coral throughout SARS, and
the dominant species on leeward reef crests and slopes, while reef slopes and deeper coral
carpets were predominantly Porites columnaris and P. rus. Faviids (Goniastrea and
Echinopora) were the next most abundant corals, especially in areas that had experienced a
disturbance, although these were small (most <15 cm diameter) and made up a small fraction
of the total live coral cover. Multi-specific Acropora assemblages often formed large thickets,
but these were restricted in distribution. Pocillopora was the dominant taxon in Yanbu,
widespread in Al Wajh, and much less common in northern and southern sites. Coral cover
throughout the region averaged about 20 %, with higher cover (often >50 %) in shallow water
and rapid decline with increasing depth. In each region, many reefs (15–36 %) showed signs
of damage and had less than 5 % live coral cover. These degraded sites were characterized by
extensive dead skeletons in growth position, substrates colonized by thick mats of turf algae
and soft corals (Xenia), and surviving massive and plating corals that were subdivided by
partial mortality into numerous small (<10 cm) ramets. Mortality was attributed to bleaching
events, disease, and outbreaks of corallivores occurring over the last 10–15 years. Several sites
also exhibited signs of recent mortality from crown of thorns sea stars (Acanthaster), coraleating snails, and coral disease. In many cases, the Porites framework had been recolonized by
A.W. Bruckner (&) A.C. Dempsey
Khaled bin Sultan Living Oceans Foundation, 8181 Professional
Place, Landover, MD 20785, USA
e-mail: [email protected]
N.M.A. Rasul and I.C.F. Stewart (eds.), The Red Sea,
Springer Earth System Sciences, DOI 10.1007/978-3-662-45201-1_27,
© Springer-Verlag Berlin Heidelberg 2015
471
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A.W. Bruckner and A.C. Dempsey
faviids, acroporids, and other corals and these had subsequently died. Most degraded areas
appeared to be rebounding, as substrates had high cover of crustose coralline algae (CCA),
little macroalgae, and high numbers of coral recruits and juvenile corals.
Introduction
The Red Sea contains unique, biologically diverse coral
reefs that exhibit striking contrasts in their biology, environmental attributes, and degree of human influence. The
reefs form part of the greater Indo-Pacific region and are the
most biologically diverse reef communities outside of the
southeast Asia coral triangle. Coral species overlap with
Indian Ocean fauna and also contain about 10 % endemic
species, with over 260 reported coral species in 68 genera
and 16 families (Sheppard et al. 1992). The small geographic
range of several species suggests long periods of isolation,
its extreme environment, and the limited exchange that
occurs through the Bab-al-Mandab Strait (Persga 2006). Red
Sea coral reefs are some of the most northerly reef communities and are subjected to harsh climatic conditions
including temperature and salinity extremes and high solar
radiation (DeVantier and Pilcher 2000). Inflowing surface
currents and winds vary seasonally, affecting water temperature, salinity, upwelling, and wave action and exchange
with the Indian Ocean (Behairy et al. 1992). The Red Sea is
also unique for having unusually warm temperatures that
extend throughout the water column.
Most of the Red Sea is characterized by fringing coral reefs
that extend nearly 2,000 km from the Gulfs of Suez and Aqaba
in the north to Bab-al-Mandab and Gulf of Aden in the south
(Persga 2006). Fringing reefs form a narrow border a few
kilometers wide along the shoreline and surrounding islands,
dropping steeply into the depths of the Red Sea. Fringing reefs
are 5,000–7,000 years old (Behairy et al. 1992) and largely
formed by a framework of Acropora and Porites corals.
Off much of Saudi Arabia, the coastal shelf is wider and it
supports extensive sea grass, coral reef, and mangrove habitats, with shallow reef communities found from the shoreline
to distances of up to 50–100 km offshore (Bruckner et al.
2011a). These areas support a wide range of reef morphologies, including barrier reefs, platform reefs, patch reefs, and
atoll-like tower reefs. The offshore reef formations are unusual
in that they defy classic (i.e., Darwinian) coral reef classification schemes. Their development is attributed to (1) the high
levels of tectonic activity that characterize the area, (2) salt
diapirs, (3) hyper-arid climate punctuated by extreme rainfall
events during low sea-level stands, and (4) sediment delivery
through wadis and other drainage basins (Bruckner et al.
2011a; Rowlands et al. 2014). The wide range of environmental conditions, latitudinal gradient, and the underlying
geologic structure all contribute to the development and
persistence of these highly variable coral habitats (Bosence
2005). Their future survival may be integrally linked to the
degree of anthropogenic influences.
Human pressures associated with two centuries of rapid
industrialization and precipitous economic growth increasingly threaten the fragile coral reef environments of the Red
Sea. According to the 2011, Status of Coral Reefs of the
World, the Red Sea is extremely vulnerable to environmental
threats posed by large coastal populations, overfishing, pollution, and coastal development (Burke et al. 2011). Nearly
60 % of the reefs in the Red Sea are at risk from landfilling
and dredging, port activities, sewage and other pollution, and
tourism (Burke et al. 2011). Global stressors associated with
climate change are also predicted to have major compounding impacts on Red Sea coral reefs. Mass coral mortality
occurred due to bleaching in the central to northern Saudi
Arabian Red Sea in late 1998 (DeVantier and Pilcher 2000),
but most showed promising signs of recovery a decade later
(Wilkinson 2008). In 2005, coral reefs were reported to be
generally in good condition, with 30–50 % live coral cover at
most locations and more than 50 % total cover on average at
5 m depth (Persga 2006). While no bleaching was noted
between 2006 and 2009, a mass bleaching event occurred in
central Saudi Arabia in 2010 (Riegl et al. 2013). Thermal
stress and ocean acidification are projected to increase threat
levels up to nearly 90 % by 2030; by 2050, these climate
change impacts, combined with current local impacts, will
push all reefs in the Middle East to threatened status, with
65 % at high, very high, or critical risk (Burke et al. 2011).
This chapter provides an overview of the current status of
reef-building corals on different reef systems throughout the
Saudi Arabian Red Sea, with emphasis on five regions with
prominent offshore reef systems. The distribution, abundance, cover, population structure, and condition of corals are
compared within and among these five regions. A detailed
description of the major biotic threats affecting the coral
communities is also presented. The data included in this
report represent a collaborative effort of multiple scientists
that participated in a four-year research mission conducted by
the Khaled bin Sultan Living Oceans Foundation.
Methods
Coral community structure was examined on 129 reefs in
five regions (Fig. 1) including Ras Al-Qasabah (n = 19), Al
Wajh (n = 21), Yanbu (n = 11), the Farasan Banks (n = 56),
The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea
473
Fig. 1 Five major areas
examined by the Khaled bin
Sultan Living Oceans Foundation
during the four-year research
mission. Base image provided by
Google
and the Farasan Islands (n = 22) (Fig. 2). On each reef,
depth-stratified surveys (3–5, 10–12, and 15–20 m) were
conducted using photographic transects, belt transects, and
quadrats. Four measures were recorded for corals: (1) coral
cover; (2) coral taxa (to genus) and growth form; (3) coral
size class distributions; and (4) coral condition (extent of
mortality and cause of mortality) (Table 1). The abundance,
size, and amount of partial mortality (subdivided into recent
and old mortality) of all corals 4 cm or larger in size
(recorded to genus) were assessed along either 10 m by 1 m
or 25 m by 1 m belt transects using a 1-m bar marked in
1-cm intervals for scale. Sampling for corals smaller than
4 cm was done using a minimum of six 25 by 25 cm
quadrats per transect, with each quadrat located at predetermined intervals (e.g., at 0, 5, 10, 15, 20, and 25 m).
Measurements varied slightly among sites, depending on the
observer. Coral size was measured to the nearest cm on reefs
examined in Ras Al-Qasabah, Farasan Islands, and Farasan
Banks, while corals assessed in Al Wajh and Yanbu were
lumped into six size classes. Coral abundance is presented
for each taxon as a percent of all corals recorded within
transects and the total planar surface area occupied by that
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A.W. Bruckner and A.C. Dempsey
Fig. 2 Location of study sites
within each of the five regions.
a Ras Al-Qasabah; b Al Wajh;
c Yanbu; d Farasan Banks;
e Farasan Islands. For GPS
coordinates of sites, see Bruckner
(2011b)
taxa. Planar surface area was calculated by multiplying the
square of the radius by pi.
For all phototransects, benthic community composition,
including cover and size (planar surface area) of corals,
cover of other animals (subdivided into soft corals, sponges,
and other invertebrates), cover of algae subdivided by
functional group (turf, macroalgae, crustose coralline algae,
erect coralline algae, and cyanobacteria), and substrate type
(rubble, sand, and uncolonized pavement) were assessed
using coral point count (CPCE) software developed by the
National Coral Reef Institute (NCRI). Cover was determined
by recording the benthic attribute located directly below a
random point, with 30–50 points per photograph (depending
on the size of the image; for example, 30 points for a 0.5-m2
photograph and 50 points for a 1-m2 photograph). This
software also allowed tracing of the outline of individual
corals to determine their planar surface area and size of live
versus dead portions of the colony.
Results
Coral Community Structure
A total of 55 genera were recorded in the 5 regions. The
Farasan Banks exhibited the highest diversity (54 genera),
followed by Al Wajh (52), Yanbu (49), Farasan Islands (46),
and Ras Al-Qasabah (44). The spatial distribution of the
The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea
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Table 1 Resilience assessments for stony corals included in SARS surveys
Measure
Description
Stony coral
Genus-level identification of the composition, abundance, cover, size structure, condition, and level of recruitment
within representative habitats
Taxa and growth form
The diversity and structural complexity of a site. Communities with higher numbers of functional groups (e.g.,
acroporids, faviids, pocilloporids, and poritids) and growth forms (e.g., branching, plating, massive corals), and
redundancy of these groups may support more associated species and be more resilient
Cover
Measure of amount of living coral. Small changes in cover are difficult to document, but abrupt changes may reflect a
major disturbance
Size structure
Maturity and ecological state of the taxa. Dominance of large corals may be a sign of stable environmental conditions
and long-term persistence of the community; a dominance by small corals suggests frequent disturbance or
recovery from a recent disturbance
Recruitment
Abundance of recruits reflects the reef’s potential for growth and recovery after major disturbances and the influx of
genetic diversity
Fragmentation
Level of physical disturbance and potential for asexual propagation. Locations of fragments (accumulations in sand
channels or on reef) and fragment condition (no tissue loss; fusion to the substrate; presence of new growth)
reflects the potential survival and contribution of fragments to recovery
Dead standing coral
Amount of dead standing coral can be used to hindcast past disturbance events up to a decade or more
Old mortality
Presence of dead areas on corals that are colonized by other biotic agents (e.g., skeleton is not white). Species-specific
differences reflect the life history strategies, population dynamics and susceptibility to various physical and
biological factors. Old mortality may increase with colony size
Recent mortality
Extent of recent mortality (white skeleton) reflects the severity, timing, and duration of a stressor. Large white areas
indicate rapid ongoing tissue loss, while a thin band of white skeleton and a wide band of green, algal-colonized
skeleton suggests the event is near its end
Bleaching
Reef-wide bleaching may be associated with recent or ongoing temperature anomalies; extent of recent mortality
indicates the duration and severity of the temperature stress
Disease
Spatial patterns of disease reflect potential for spread and level of contagion. Distinction between background
mortality (chronic stressors) and of disease outbreaks (acute mortality)
Corallivores
Abundance of coral predators (Drupella and Coralliophila snails, Acanthaster sea stars) indicative of the amount of
recent mortality and possible changes to coral community structure and species diversity due to chronic high-level
infestations or outbreaks
Competition and
overgrowth
Negative factors inhibiting the growth and recovery of corals and causes of chronic mortality (e.g., algal competition)
and bioerosion (e.g., sponges). Extent and composition of competitor may reflect status of fish communities
(herbivores), nutrient loading, and sedimentation
Coral associates
Obligate corallivores (butterflyfish) provide an indication of the health of the coral community or a particular taxa
Abundance and diversity of fishes and invertebrates within coral branches are indicative of the topographic complexity
and health of the site
An abundance of territorial damselfish within branches and large algal lawns indicate possible overfishing of
piscivores
High densities of sea urchins may be associated with extensive bioerosion of reef substrates and low recruitment and
survival of newly settled corals; macroalgae may increase in with the absence of sea urchins, especially sites with
few herbivorous fishes
dominant coral species varied by region, site, and habitat/
depth. The dominant genera throughout all sites were Porites
and Acropora, with P. lutea being the single most common
species (Fig. 3). On offshore habitats in the central Red Sea,
the three consistently dominant coral genera over all pooled
sites were Acropora (average cover over all transects 3 %),
Porites (2.75 %), and Pocillopora (1.3 %). Large monospecific assemblages of Pocillopora were found on shallow
fore-reefs in Yanbu; this genus was present but not among
the five most dominant species in Al Wajh and Farasan
Banks and was rare in Ras Al-Qasabah and Farasan Islands.
In Al Wajh, Montipora was the second most abundant
genera, primarily on offshore reefs, while branching and
table acroporids were most common on inshore and turbid
reefs. Acroporids were only rarely seen on offshore sites of
Al Wajh, with the exception of small digitate acroporids and
tightly branched, low-lying colonies in reef crests and
shallow fore-reefs (Fig. 3b).
Tabular acroporids formed dense thickets in shallow water
(<8 m) on offshore sites at the northern and northwestern end
of the bank system in the Farasan Islands, while dense Acropora communities were found throughout nearshore and
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Coral Cover
Fig. 3 Relative abundance and area occupied by all of the coral genera
identified within belt transects. Each genus is illustrated as a percent of
all genera recorded and the total estimated planar surface area of all
corals in that genera. a Ras Al-Qasabah; b Al Wajh; c Yanbu;
d Farasan Banks; e Farasan Islands
midshelf locations in the Farasan Banks; Acropora was rare
overall in Ras Al-Qasabah. Coral assemblages on offshore
vertical walls either formed encrusting, foliaceous, and platelike colonies of Montipora, Echinopora, Pavona, Turbinaria, Leptoseris, and Pachyseris, or small submassive colonies, such as Stylophora marmorata; 22 % of offshore
locations had large dead stands of foliaceous corals still in
growth position. Small Goniastrea colonies (recruits and
remnants) were the most abundant coral in lagoonal areas of
Al Wajh and throughout Ras Al-Qasabah, especially where
most of the Porites colonies had died.
The benthic environment in most locations was dominated
by scleractinian corals, which were highest at the Farasan
Banks (mean cover = 29.4 % ± 13.4 SE; range across
sites = 4–60 %) and was lowest at Ras Al-Qasabah (mean
cover = 20.4 % ± 10.4 SE; range = 2–40.1 %) (Fig. 4). Dead
standing corals also comprised a significant portion of the
total cover (mean cover = 10.4 % across all sites). Between
15 and 36 % of sites in each region showed signs of damage
and had significantly less living coral cover (1–5 %) and
higher cover of dead standing skeletons (14–20 %). This
included all of Ras Al-Qasabah, most lagoonal reefs in Al
Wajh, and several remote midshelf and offshore locations in
Yanbu, the Farasan Banks, and the Farasan Islands.
In all regions except Ras Al-Qasabah, coral cover was
usually the highest in the shallow reef crest and fore-reef on
outer fore-reef locations (1–5 m depth; 30–70 %). Coral
cover declined with depth, with 20–30 % cover at middepths
(7–12 m depth), and <5–30 % at the base of the reef slope
(15–30 m), especially on midshelf and outer sites.
Throughout the Saudi Arabian Red Sea (SARS), Porites
made up 25 % or more of the living coral cover and over
80 % of the coral cover in the Farasan Banks. The cover of
Acropora exceeded Porites only in the Farasan Islands,
mainly due to the dominance of large colonies on offshore
locations (Fig. 7b). In all locations, the substrate and dead
skeletons were carpeted in soft corals (predominantly
Xenia;14–20 % cover), encrusting sponges, and other noncoral invertebrates, especially in degraded areas and on
deeper reefs (>20 m depth), and these were often competing
with hard corals for space and overgrowing surviving remnants. Deep (>20 m) offshore reefs in the Farasan Banks also
had low cover of scleractinian corals and large assemblages
(30–50 % cover) of organ pipe coral (Tubipora musica).
Shallow locations in the Farasan Islands, nearshore reef flat
communities in Farasan Banks, and areas in Ras Al-Qasabah
had high cover of macroalgae and moderate cover of turf
algae and crustose coralline algae, while macroalgae were
rare elsewhere (Fig. 4).
Coral Size Structure
Corals in all locations were mostly small in size (over
90 % <20 cm diameter), with medium-sized corals
(20–40 cm) making up most of the cover (Fig. 5). These
differences are due to the non-linear relationship between
coral size and surface area as a result of a very high numerical
abundance of recruits, juvenile corals, and tissue remnants.
Recruits and juvenile corals (<5 cm diameter) were more
The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea
477
Fig. 5 The total abundance of corals per size class and the total colony
area for all scleractinian corals (pooled species). a Ras Al-Qasabah;
b Al Wajh; c Yanbu; d Farasan Banks; e Farasan Islands
Fig. 4 Benthic cover subdivided into live coral cover, dead coral, algal
functional groups (macroalgae, turf algae, crustose coralline algae, and
cyanobacteria), benthic invertebrates (soft coral, sponges, and all other
invertebrates, pooled), and rubble and uncolonized substrate (sand and
pavement). a Ras Al-Qasabah; b Al Wajh; c Yanbu; d Farasan Banks;
e Farasan Islands
abundant than all other size classes at Al Wajh (48 % of all
corals; Fig. 5b), Yanbu (44 %; Fig. 5c), and Farasan Banks
(38 %; Fig. 5d). Although small corals dominated numerically in these locations, most of the cover consisted of
30–40 cm diameter colonies at the Farasan Banks and
21–80 cm at Al Wajh, while much larger corals (40–160 cm)
made up most of the cover at Yanbu. Ras Al-Qasabah
(Fig. 5a) and the Farasan Islands (Fig. 5e) had much lower
numbers of recruits and juveniles. Even though Ras Al-Qasabah was dominated by small corals (most corals were 6–
9 cm diameter with 10–20 cm colonies making up most of the
cover), these tended to be surviving tissue remnants on much
larger skeletons. While 3–20 cm colonies were most numerous in the Farasan Islands, the bulk of the cover consisted of
colonies that were 30–75 cm. The mean colony size also
varied greatly between taxa. The largest corals overall were
Porites and Acropora, with low numbers of very large (>1 m)
Diploastrea, Galaxea, and Montipora colonies seen in some
locations, while faviids (Favia, Favites, Platygyra, Leptastrea, and Cyphastrea) tended to be small (<10 cm). The size
structures for the four most abundant genera (Porites, Acropora, Goniastrea, and Echinopora) are shown in Fig. 6.
478
A.W. Bruckner and A.C. Dempsey
recruiting faviids, which have comparable growth rates to
Porites, nevertheless covered less space on the reef. Almost
the entire encountered Leptastrea population consisted of
small colonies. Although Montipora recruited more frequently than Acropora and also has a high growth rate, it
was found to cover far less space on the reefs.
Coral Condition
Fig. 6 Size frequency distribution of the four dominant genera of
corals and all other species pooled. a Ras Al-Qasabah; b Al Wajh;
c Yanbu; d Farasan Banks; e Farasan Islands
Coral Recruitment
Coral recruitment was lowest at Ras Al-Qasabah and the
Farasan Islands, with moderate levels of recruitment documented at fore-reef sites in Yanbu and both barrier reef and
lagoonal sites at Al Wajh. The Farasan Banks had the
highest recruitment overall, especially in degraded sites; an
average density of 3.3 ± 1.7 juvenile corals (<4 cm diameter)
per quadrat and *13 juvenile corals (>4 cm diameter) per
m2 was documented. Poritids were the most common
recruiters (26 %), followed by the faviids (20 %), Pavona
(12 %), and the acroporids (11 %). Seven genera made up
three quarters of all recruits (74.7 %). The distribution of
recruitment frequency reflected the dominance of large
corals: Porites recruited more commonly than Acropora and
also covered more space on the reefs. The commonly
The three major factors responsible for coral mortality
identified in SARS are coral bleaching, coral disease, and
corallivory. Coral bleaching was rare during the assessments
with exception of mild bleaching in 2006, at Ras Al-Qasabah. Coral diseases were identified in all locations, although
prevalence was generally low. The most common coral
diseases reported for the Indo-Pacific were observed in this
study, including white syndrome, brown band, yellow band,
skeletal eroding band, and black band disease. Several colonies had sustained extensive partial mortality from diseases,
suggesting that diseases play a key role in reef degradation
(Fig. 7).
Coral predation appeared to be the most significant
chronic source of mortality affecting these reefs (Fig. 8). In
particular, localized outbreaks of Drupella snails and crown
of thorns starfish (COTS) were noted. Active COTS outbreaks were observed in the Farasan Islands, Al Wajh
(lagoonal sites only), and the Farasan Banks, but not in Ras
Al-Qasabah. COTS counts ranged from 10 to 498 animals
per 100 m2, with highest densities and the highest number of
affected reefs at the Farasan Banks. In the Farasan Banks,
nearly 20 % of the sites had sustained near total mortality of
adult corals prior to these surveys, and extensive recent
mortality at other sites was attributed to ongoing COTS
outbreaks. At low density, COTS preferred acroporid corals
as a food source and fed only occasionally on poritids. In
areas with high densities (Farasan Banks), no prey preference was observed and most taxa were equally affected. At
sites that were subjected to intensive COTS depredation in
the past, Diploastrea heliopora was the only large coral
(diameter *1 m) that had survived, with high numbers of
small (10–20 cm diameter) massive colonies of Echinopora
and isolated tissue remnants of Goniastrea. Several sites that
had been damaged prior to these surveys also exhibited
extensive mortality on the deeper parts of the fore-reef
(>5 m) while healthy coral communities remained in shallow
water (2–5 m), suggesting that damage was not due to past
bleaching events. Lesions from coral-eating snails (Drupella) were observed frequently on Pocillopora, followed by
Acropora, while Porites and faviids were mostly affected by
Coralliophila. In general, Drupella caused large patches of
tissue loss that expanded across the corals in a band-like
manner while Coralliophila typically inhabited depressions
The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea
Fig. 7 Coral diseases observed in the Red Sea. a Growth anomaly
(hyperplasia) on Acropora gemmifera. b White syndrome on Ctenactis
echinata. c Black band disease on Favites spp. d Tumors (neoplasia) on
a table Acropora. e White syndrome on Acropora hyacinthus. f Black
band disease on Echinopora. g Skeletal eroding band on Goniastrea.
479
h Undescribed multifocal lesion on Goniastrea. i Pink line disease on
Porites lutea. j Skeletal eroding band on Goniastrea. k Ulcerative
white spots (PUWS) on Porites. l Pink line disease on Porites. m White
syndrome on Favia. n Brown band disease on Acropora. o Dark spots
disease on Goniastrea
480
Fig. 8 Characteristic signs of predation observed in the Red Sea.
a Coralliophila gastropods feeding on Porites. b Drupella gastropods
feeding on Pocillopora verrucosa. c Stylophora with gastropod
predation. d Close-up of Drupella snails on Acropora. e Acanthaster
(crown of thorns starfish) feeding on Echinopora. f COTS feeding on
A.W. Bruckner and A.C. Dempsey
Porites. g, h, and j Damselfish algal lawns on Porites and Platygyra.
i Spot biting by parrotfish on Porites. k Pocillopora with branch ends
bitten off by parrotfish. l, m, n, and o Focused biting by parrotfish on
Leptoria, Galaxea, and Porites
The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea
481
Fig. 9 Nuisance species. a Fan
sponge (possibly Phyllospongia)
that commonly overgrows corals
in the Farasan Islands and Farasan
Banks, shown here covering a
Porites lutea. b Xenia, a soft coral
that monopolizes substrate,
overgrows corals, and inhibits
recruitment. Xenia was a
dominant constituent of deeper
reef communities throughout the
SARS and is seen here
overgrowing a Porites lutea in the
Farasan Islands. c Unidentified
encrusting sponge that covered
large areas of reef and overgrew
corals in deeper locations in the
Farasan Banks. d Mat of Palythoa
(colonial zoanthids) overgrowing
Porites lutea. e Cyanobacterial
mat on a colony of Goniastrea.
f Encrusting/bioeroding sponge
killing a Porites lobata colony.
g Brown macroalgae covered
large portions of reef flat
communities in nearshore and
southern localities. h Millepora
hydrozoan coral overgrowing
Galaxea
in a colony, especially between lobes, and only rarely caused
visible tissue loss. Drupella appeared to control the upper
size limit of Pocillopora colonies in Yanbu, as most corals
over 10 cm were infested with snails and few intact colonies
over 20 cm were found.
A number of nuisance species (e.g., Xenia, clionid
sponges, encrusting sponges, leather coral, Millepora, zoanthids, and Peyssonnelia brown algae) competed and
overgrew corals and monopolized substrates. Throughout
SARS, the deeper Porites framework was largely dead and
most of the skeletons were carpeted in mats of Xenia. In the
Farasan Banks and Farasan Islands, encrusting sponges often
formed large mats on open substrates and they were frequently observed overgrowing and bioeroding corals. Macroalgae were generally uncommon, but in parts of Ras
Al-Qasabah, shallow nearshore sites in the Farasan Banks,
and throughout the Farasan Islands, a substantial amount of
substrate was colonized by macroalgae. Damselfish algal
lawns were especially common in areas with few predatory
fishes (Fig. 9).
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Discussion
The assessments conducted in the Saudi Arabian Red Sea,
including measures of coral diversity, size structure, condition, causes of mortality, and other benthic attributes present
a first indication of the status, vulnerability, and resilience of
these reefs. Knowledge of the demographic structure of a
coral population can provide insight into the effects of disturbance and resilience of reefs. Coral populations are normally highly positively skewed, with dominance by the
smallest size classes and an exponential decrease with
increasing colony size (Bak and Meesters 1998, 1999). Larger colonies typically become rarer in a population, but they
have a decreased probability of total colony mortality relative
to smaller colonies (Hughes and Jackson 1985; Soong and
Lang 1992). One consequence of this is that smaller colonies
suffer total mortality more frequently than larger colonies,
while larger colonies sustain higher levels of partial mortality
over multiple disturbances, but have a greater chance of
survival (Babcock and Mundy 1996; Hall and Hughes 1996).
Thus, size frequency distributions of coral populations are
key indicators for categorizing changes in coral communities
in response to acute and chronic disturbances and may help
identify differences between populations exposed to differing
degrees of environmental stressors.
In addition to differences in survival, colony size is an
indicator of the reproductive potential of the population.
Corals show a positive relationship between colony size and
fecundity, with smaller colonies allocating more energy to
growth and maintenance and focusing on reproduction only
after achieving a critical threshold size (Szmant-Froelich
1985; Harrison and Wallace 1990). Reproductively mature
colonies may also regress in size below that minimum
threshold, becoming non-reproductive (Szmant 1991).
Competitive abilities and regenerative potential also increase
with size (Meesters et al. 1994). By combining size structure
with estimates of mortality, it is possible to predict whether a
population is more likely to continue to contribute to
recruitment. A reef consisting of healthy, larger, older colonies with low levels of partial mortality is likely to produce
higher numbers of gametes than a reef dominated by juveniles or older colonies with high levels of partial mortality. A
population dominated by small size classes may indicate
high mortality in intermediate and larger corals (Nyström
et al. 2008). Large colonies that have been reduced into
tissue isolates that are below the minimum size needed for
reproduction may expend more energy on growth and
maintenance and less on reproduction (Bruckner 2012).
In SARS, knowledge of the extent of partial and whole
colony mortality provided an indication of the severity of past
disturbances, resistance of the corals, how much recovery has
occurred, and the likelihood that the reef will survive future
disturbances. For instance, several offshore reefs in Al Wajh
A.W. Bruckner and A.C. Dempsey
were dominated by large, massive Porites colonies with few
juveniles; these areas likely have not experienced a recent
large-scale disturbance. This suggests that, despite what
appears to be a fairly stable community, these reefs may lack
resilience to future disturbances, as new corals are not settling
or replacing older colonies. Most reefs in Ras Al-Qasabah and
lagoonal reefs in Al Wajh had few large corals, several canopy
layers of dead corals in growth position, and a high abundance
of small tissue remnants, suggesting these reefs have been
perturbed very frequently. In contrast, a large number of
midshelf and offshore reefs in the Farasan Banks had few large
corals, high numbers of skeletons in growth position, and an
unusually high number of recruits, indicating a mass die-off
from a previous disturbance, with signs of rapid recovery.
Ras Al-Qasabah
Reefs throughout the region showed evidence of a past (10–
15 years) mortality event that affected 50–75 % of the corals
and was responsible for the loss of most of the columnar
Porites colonies. The Porites framework was subsequently
colonized by acroporids, faviids, and Lobophyllia in shallow
water, and foliose and plating Echinopora and Turbinaria
colonies in deeper water but most of these corals had 3–
9 years before these surveys, and skeletons remained in
growth position. Living coral cover is now lower than in all
other regions; surviving corals include highly fragmented
remnants of large Porites colonies, small massive faviid
corals (Goniastrea and Echinopora) and encrusting Montipora and branching corals (primarily Stylophora and Seriatopora). There were also high cover of Millepora, Xenia,
and Peyssonnelia, large areas of uncolonized reef framework, and considerable amounts of rubble.
Coral bleaching events appear to be the major stress
responsible for extensive losses of coral at Ras Al-Qasabah.
First, extensive mortality was apparent in all sites and depths
including shallow water, unlike other regions examined in this
study which had prolific coral growth in shallow water (1–
5 m) and mortality restricted to middepth and deep sites.
Furthermore, during the four-year mission, bleaching was
only documented in Ras Al-Qasabah. One contributing factor
is that the region is exposed to temperature extremes and it
lacks the protective buffering afforded by the upwelling of
cooler waters because the eastern boundary current that flows
northwards up the Saudi coastline may suppress wind-driven
upwelling of deep water. Mortality will therefore be higher
than expected during periods of unusual thermal anomalies
and more severe than the relatively more healthy neighboring
Tiran area (Ras Qisbah) off the Sinai Peninsula. Sites at the
edge of the platform along the extensive bank and reticulate
reef systems were also affected by pooling of water over
shallow reefs, and high outflows of sediment and super-heated
The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea
water may prevent recovery of these sites and exacerbate the
impacts of future bleaching events. The richest coral cover and
diversity remain in areas near channels, as tide-driven flow
through restricted channels promotes flushing
Al Wajh and Yanbu
The coral community structure at Yanbu and Al Wajh was
dominated by small tissue remnants of Porites columnaris
and high numbers of recruits and juveniles of Acropora,
Montipora, Goniastrea, Favia, and Pocillopora. Although
the sites show evidence of a past mortality event, they appear
to have stabilized and are now recovering. While many of
these reefs are vulnerable to future perturbations, they also
show high resilience. Al Wajh has an extensive bank and
barrier reef system, and an unusually large lagoonal system
with a high number of shallow and differentiated habitats
(e.g., grassbed, mangrove, patch reef, and fringing reef). The
highest coral cover occurred on the barrier reef and on reefs
located near channels, while most lagoonal patch reefs
exhibited low cover. The lagoonal reefs appear to have
experienced a mass mortality event 6–9 years before these
surveys were completed, with coral communities dominated
by small, fragmented tissue remnants along with a moderate
number of faviid, poritid, and acroporid colonies. These disturbances appear to have affected many of the important
framework corals, as evidenced by the extensive amount of
dead coral and bioerosion of these colonies. Lagoonal habitats
are likely to experience more highly fluctuating temperatures
in the shallows, higher sediment transport, lower visibility,
stronger/more variable currents, a greater degree of ponding
of waters, and moderate to high levels of turbidity. The reefs
at Yanbu include extensive shallow coastal marine habitats
with large stands of mangroves, submerged grass beds, and a
complex offshore barrier reef system consisting of a string of
linear reef complexes parallel to the coast and separated by a
major shipping channel. Water temperatures are likely to be
cooler on offshore sites due to the steeper linear slopes, and
thus, bleaching impacts will be less severe. Shading by the
reef structure was pronounced; the linear reef system runs
north/south, with a high degree of shading on vertical faces
and slopes, particularly for the steeper west-facing slopes in
the morning. Yanbu’s reefs as well as the outer barrier reef
sites of Al Wajh are both likely to be exposed to high wave
energy and have few sheltered locations.
Farasan Banks
The Farasan Banks contain the most extensive and diverse
reef environments in SARS, with fringing reefs along the
mainland coast, nearshore algal reefs, circular or elongated
483
patch and platform reefs, barrier reefs, coral pinnacles, and
emergent or submerged atoll-like structures. Shallow and
deeper reef habitats were dominated by a high cover of
living Porites. These taxa was both numerically dominant
and often the largest corals in the population, although
nearly one-third of the sites examined contained large areas
of dead Porites framework as well as signs of recent mortality from disease and predation. Nevertheless, most mortality was patchy and restricted to middepth and deeper
locations, while shallow sites often had 50–70 % living coral
cover, suggesting bleaching played a minor role in disturbances. The site experiences large latitudinal and seasonal
extremes in temperature, and above-average salinities, two
factors that would typically contribute to high mortality of
corals. Still, the presence of flourishing coral communities in
many of the sites suggests local populations are well adapted
to temperature-induced stress, with local environmental
extremes likely to be close to their physiological tolerance
maxima. In this case, local coral populations may be particularly vulnerable to climate change.
On a positive note, the midshelf and offshore reefs in
most sites were surrounded by deep water and strong currents (seasonally changing direction) and exhibited numerous physical attributes (such as steep vertical walls and
overhangs) that are likely to moderate temperature extremes.
Furthermore, turbid conditions on nearshore reefs reduce
UV penetration, also mitigating the potential for coral
bleaching. Although many sites appeared degraded, with a
near total loss of adult colonies, the region exhibited
numerous additional factors that confer resilience. First, the
number of coral recruits was 2–10 times higher than that
observed elsewhere in the Red Sea and up to 100 times
higher than that reported from adjacent areas in the Indian
Ocean. Secondly, substrate quality was high and conducive
to coral settlement, with low amounts of unstable rubble,
very low macroalgal cover, relatively low cover of soft
corals, and higher amounts of crustose coralline algae than
observed in other areas along the Saudi Arabian Red Sea
coastline.
Farasan Islands
Coral communities in the Farasan Islands were largely
restricted to windward and leeward coral crests, located
seaward of the major islands, while nearshore habitats were
largely algae-covered pavements, sand flat communities,
seagrass meadows, mangroves, patch reefs, and macroalgaldominated fringing reefs. Live corals typically formed small
patches in shallow water (<8 m) surrounded by rubble fields
and sediment covered algal pavements, with low cover of
living corals in deeper water, except for offshore locations.
Most of the sites with the highest living coral cover were
484
located to the west and northwest of Farasan Kabir, especially those sites on Al Baghlah Bank, Massad Island,
Shuma, and Lajhan. Located far offshore, they have much
less siltation than nearshore habitats. In contrast, reefs off the
main islands, including Zufaf Island and Dushuk Island,
were much more degraded. These sites had higher abundances of soft corals, encrusting and bioeroding sponges,
macroalgae, and cyanobacteria. This community shift may
be the result of a number of stressors, namely land-based
nutrient loading and/or reduced herbivory. While many sites
showed signs of previous disturbance events evidenced by
extensive rubble, dead coral, and colonization by early
recruiting soft corals, the high proportion of small colonies
throughout these disturbed sites is indicative of the success
of recent successful recruitment events and progressive
regeneration.
Conclusion
Like elsewhere, SARS coral reefs have been subjected to
serious disturbances over the past few decades including the
1998 bleaching event (DeVantier and Pilcher 2000). Sites
examined during these surveys had been impacted by
ongoing COTS outbreaks and had clearly suffered from past
bleaching. Causes of coral mortality could be clearly identified in most cases; in other cases, low coral cover and high
numbers of dead and mostly dead colonies in growth position bore testimony of disturbances that had occurred in the
recent past (10–15 years). Impacts to these sites occurred in
all habitats and reef zones although the severity of damage
was highly variable. Many reefs appeared to have been
disturbed, undergone recovery, and then damaged again,
while others showed few signs of degradation. The variability between sites and within individual reefs, coupled
with the number of degraded reefs, suggests that local disturbances acting on individual reefs (e.g., COTs and disease
outbreaks) have been more common than region-wide (e.g.,
mass bleaching) events.
While diversity remained fairly high, the occurrence of
completely denuded reefs and low remaining species
diversity on these sites suggests that some of the rarer coral
species identified from the region during earlier studies are
likely to disappear (Sheppard 1985; Sheppard and Sheppard
1985, 1991; Devantier et al. 2000). Although coral community differentiation with regards to zone-forming genera
was still apparent throughout SARS, there appears to be a
loss of the largest colonies, especially some of the slower
growing taxa that were reported in previous studies (Kleemann 1992; Riegl and Piller 1997, 1999; Devantier et al.
2000). While numerous unusually large skeletons were
encountered, in degraded areas, surviving colonies consisted
largely of small tissue remnants. Further, there has been a
A.W. Bruckner and A.C. Dempsey
general shift from Acropora and Porites in shallow water to
faster growing Stylophora and Pocillopora, and from large
Porites to smaller faviid colonies in deep water (Riegl et al.
2013). These factors highlight an increase in community
homogenization and decline in average size of coral colonies, as reported for other parts of the Red Sea (Riegl et al.
2012).
Although these reefs have undergone extensive degradation over the last several decades, most reefs show a
promising trajectory of recovery. The dominant reef frame
builders are massive and submassive colonies of Porites.
This taxon is more tolerant to thermal stress than most other
genera and also less susceptible to mortality from disease.
Coral diseases were present, but relatively uncommon, with
exception of a disease affecting massive Porites colonies.
Several outbreaks of Acanthaster planci (crown of thorns)
were noted in midshelf reefs, and these sea stars were negatively impacting sites with the highest live cover of
branching acroporid corals.
Nevertheless, their target species are among the fastest
growing corals and they exhibited very high levels of
recruitment. A high diversity of reef-building corals exists,
including multiple growth forms and resistant taxa, many
functional groups, and a wide size range extending from the
small (juvenile and recruits) to large-sized colonies. In areas
with widespread mortality of adult corals, the dead colony
structure remained largely intact, and substrate quality was
high, with high cover of crustose coralline algae. Further, the
presence of unusually high numbers of juvenile corals and
recruitment levels that often exceeded those reported from
other locations in the Red Sea and Indian Ocean suggests
these reefs are undergoing rapid recovery. Reefs also
exhibited a number of environmental and physical factors
that confer resilience. In general, reefs in central and
southern SARS had relatively high structural complexity,
several canopy layers (which helps shade corals), low
amounts of loose rubble (which makes the substrate unstable
and reduces the settlement of corals), and little macroalgae
(which overgrows and smothers slower growing corals).
Although most damaged areas were showing promising
signs of recovery during these surveys, many areas are at a
critical threshold and could fail to recover from future disturbances. Firstly, the region is under increasing pressure
from artisanal and subsistence fisheries (Bruckner 2011a;
Bruckner et al. 2011b) and most of the fishing occurs within
the lagoon and nearshore sites, where corals are under the
greatest stress from temperature perturbations and land-based
stresses. As populations continue to expand in coastal areas,
the consequences of human threats are likely to worsen. The
presence of cyanobacterial mats, a rarity of detritivores (e.g.,
sea cucumbers), a scarcity of large herbivores, coupled with
high cover of Xenia (carpeting much of the Porites framework), increases in other nuisance species (encrusting and
The Status, Threats, and Resilience of Reef-Building Corals of the Saudi Arabian Red Sea
bioeroding sponges, damselfish algal lawns) provide strong
evidence that substrate quality may be declining. The five
regions examined in this study contain the most unique and
extensive coral reef ecosystems found in the Red Sea, and
they support extensive associated nursery habitats (e.g.,
mangroves and seagrass beds). As climate-related stressors in
the Red Sea continue to increase (Cantin et al. 2010), it is
critical that human impacts to these areas are reduced and
more consideration is given for the inclusion of these areas in
a network of marine protected areas.
Acknowledgments The four-year research mission to the Saudi Arabian Red Sea could never have been completed without the leadership,
vision, and generosity of His Royal Highness Prince Khaled bin Sultan.
We are deeply appreciative of his financial support and for the generous
use of his research vessel, M/Y Golden Shadow. His vision of Science
Without Borders® was materialized in the research mission to the Red
Sea through the partnerships and involvement by the Saudi Wildlife
Authority, Nova Southeastern University, the International Union for
Conservation of Nature (IUCN), Coastal Ocean Research and Development in the Indian Ocean (CORDIO), and Blue Ventures. Data
presented here were summarized from benthic transects conducted by
Bernhard Riegl, David Obura, Alastair Harris, and Andrew Bruckner.
All phototransects were conducted by Annelise Hagan and Philip Renaud. The Saudi Wildlife Authority (formerly the National Commission
for Wildlife Conservation and Development) under the leadership of
the Secretary General, His Excellency Prince Bander bin Saud, provided assistance to KSLOF throughout this research mission. All permits for the work were obtained through the assistance of Mr. Omar
Khushaim. None of this research would have been possible without
dedicated involvement by Captain Nick Gilbert, Captain Mike Hitch
and the devoted officers, and crew of the M/Y Golden Shadow. I am
grateful for the detailed comments provided by four anonymous
reviewers.
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